The present invention relates to magnetoresistive write/sense heads for magnetic media data storage systems. In particular, the present invention relates to a geometrical configuration of a shield in a magnetoresistive write/sense head.
Magnetoresistive sensors are employed as sense or read transducers in the write/sense heads of some types of magnetic disk drives. The electrical resistance of a magnetoresistive sensor changes depending upon the sensor's proximity to a magnetic field. Additionally, the electrical resistance of a sensor positioned in a magnetic field varies as a function of the strength of the magnetic field. A magnetoresistive sensor positioned above a magnetic data storage disk can be used to sense the magnetic fields associated with localized magnetic domains impressed upon the disk surface. This local magnetic domain represents data which the sensor reads. A magnetoresistive sensor typically comprises a thin layer of ferromagnetic material which exhibits a magnetoresistive effect, such as a nickel iron alloy. The ferromagnetic layer is deposited upon an electrically insulating substrate. Magnetoresistive sensors work best where the active region of the sensor has no magnetic domain boundaries. In other words, the active sense area of the magnetoresistive sensor should be a single domain. The presence of domain boundaries in a sensor gives rise to Barkhausen noise, a phenomena caused by the irreversible motion of magnetic domains in the presence of an applied magnetic field. Barkhausen noise cannot occur if no domain boundaries exist. Typically, a single domain magnetoresistive sensor is achieved after fabrication using a process in which the magnetization is "set" using an external magnetic setting field.
A double-gap magnetoresistive head, such as that described in U.S. Pat. No. 4,803,580 has separate write and sense gaps defined by arranging linearly a top magnetic pole, a middle magnetic pole, and a trailing shield. The top pole, the middle pole, and the trailing shield are all constructed from soft magnetic materials. The write gap is the gap between the top pole and the middle pole and the sense gap is the gap between the middle pole and the trailing shield. The magnetoresistive sensor is positioned in the sense gap between the middle pole and the trailing shield. The magnetoresistive sensor design is of a type which can support a single domain state. The middle pole and the trailing shield operate as shields for the sensor which substantially block the sensor from magnetic fields other than a magnetic field generated by a local magnetic domain positioned directly under the sense gap, such as a magnetic domain on a magnetic disk. The shielding is generally quite effective against the field strength encountered in disk drive operating environments.
The magnetic shield itself contains magnetic domains. The magnetoresistive sensor is positioned between the two magnetic shields. Consequently, the magnetic domain pattern carried by the magnetic shields can affect the operation of the magnetoresistive sensor. It is therefore important to provide a magnetic shield design which stabilizes a desired magnetic domain pattern.
However, during the manufacture of a magnetoresistive head, the head structure is subjected to external magnetic fields. The manufacturing process may subject the head to fields of sufficient magnitude to alter the domain pattern of the shield into an undesired structure. These fields may saturate the magnetic shield in the easy axis direction. Furthermore, the magnetic field generated during a write operation from the inductive magnetic write head associated with the magnetoresistive readback sensor, provides magnetic fields which can destabilize the shield's magnetic domain pattern.